The present disclosure generally relates to methods for assaying ionic materials, and, more specifically, to methods for assaying ionic materials using an integrated computational element to determine their binding state.
The analysis of ionic materials, both inorganic and organic in nature, is ubiquitous throughout numerous industrial processes. In many such cases, it can be desirable to determine the total quantity and/or types of ionic materials that are present in a fluid phase. Although some ionic materials can be readily assayed by routine spectroscopic techniques to determine their overall concentration of a fluid phase, certain types of ionic materials are much less readily analyzed by spectroscopy. For ionic materials that are not readily analyzable by routine spectroscopic techniques, their overall concentration in a fluid phase can sometimes be determined by various wet analytical techniques such as, for example, colligative property measurements and ion chromatography. For both spectroscopic and wet analytical techniques, interfering substances can be problematic for the analyses, and substantial sample preparation can sometimes be involved.
Although the total concentration of an ionic material in a fluid phase can represent a useful process diagnostic, an ionic material's total concentration may inaccurately represent the true nature of the ionic material in the fluid phase. For example, an ionic material can often be present in a fluid phase in various “complexed” or “bound” states, or it can simply be solvated by the fluid phase, the latter representing “free” or “unbound” ionic material. These groups of terms will be used synonymously herein. “Complexed” and “free” ionic materials can often behave very differently in a fluid phase, and as a result, the total ionic concentration may not be a representative diagnostic by which to judge or regulate an ongoing process. For example, a “complexed” Ionic material may be non-reactive and/or non-damaging in a process, but a “free” ionic material may be highly problematic. As a specific example, “free” metal ions may be particularly prone to scale formation in some instances. Collectively, various “complexed” and “free” ionic materials will be referred to herein as the “ionic species” or “binding states” of an ionic material.
Although certain ionic materials can be readily analyzed by spectroscopy to determine their overall concentration in a fluid phase, it can sometimes be much more difficult to determine the various fluid phase binding states of the ionic material, particularly by spectroscopy. If different regions of a spectrum can be conclusively identified as being produced predominantly by a particular binding state of an ionic material, an estimated binding state distribution can be obtained. However, the spectral differences between ionic materials in various binding states are often not well distinguished from one another by conventional spectroscopy, and the ability to successfully deconvolute a spectrum to determine the presence of various binding states can often be a matter of chance. Even when spectral deconvolution is possible in principle, the analyses can be costly, time-consuming, and extremely sensitive to the presence of interfering substances. Moreover, conventional spectroscopic instruments often require precise calibration and controlled operating conditions that can sometimes be unsuitable for field or process environments.